Question

The depth of penetration decreases, if

• A. Conductivity decreases
• B. Relative permeability decreases
• C. Frequency increases
• D. Phase velocity decreases

Hint:

Skin depth decreases when: \[ f \uparrow,\quad \mu \uparrow,\quad \sigma \uparrow \]

Answer 1

The Correct Option is C

Concept: Skin depth (depth of penetration) is \[ \delta = \sqrt{\frac{2}{\omega\mu\sigma}} \] where \[ \omega=2\pi f \]

Step 1: Observe the dependence.
\[ \delta \propto \frac{1}{\sqrt{f}} \] Thus skin depth decreases when frequency increases.

Step 2: Physical interpretation.
At higher frequencies, current tends to flow closer to the conductor surface. Therefore penetration depth becomes smaller.

Step 3: Final Answer.
\[ \boxed{\text{Frequency increases}} \] Hence, \[ \boxed{\text{Correct Option (C)}} \]